CDMA subscriber unit having an improved antenna system

ABSTRACT

A CDMA subscriber unit includes an antenna system having multiple antennas and delay units for receiving a transmitted signal and outputting a combined signal having a known distortion imparted by the antenna system. The combined signal is in turn processed by a modem, which compensates for the known distortion in a manner which provides improved signal gain. The improved signal gain permits a reduction in transmit power and, accordingly, increased capacity of the base station. Where the antenna system is to be remotely located from related signal processing equipment, separate units for the RF receiver/transmitter and the other signal processing equipment are provided so that the RF receiver/transmitter may also be remotely located along with the antenna system.

Cross Reference to Related Applications

[0001] This application is a continuation of application Ser. No.09/854,725; filed on May 14,2001; which is a continuation of applicationSer. No. 08/961,482; filed on Oct. 31, 1997, which issued as U.S. Pat.No. 6,259,687 on Jul. 10, 2001.

BACKGROUND

[0002] The present invention relates to wireless digital communicationsystems. More particularly, the present invention relates tocommunication stations which employ code-division multiple access (CDMA)technology wherein the station has multiple antennas for increasing thecapacity of the CDMA system.

[0003] Over the last decade consumers have become accustomed to theconvenience of wireless communication systems. This has resulted in atremendous increase in the demand for wireless telephones, wireless datatransmission and wireless access to the Internet. The amount ofavailable RF spectrum for any particular system is often quite limiteddue to government regulation and spectrum allotments. Accordingly, theneed to utilize one's allocated RF spectrum efficiently is desired.

[0004] CDMA communication systems have shown promise in the effort toprovide efficient utilization of the RF spectrum. At least one brand ofCDMA systems, Broadband Code Division Multiple Access™ or B-CDMA™communication systems available from InterDigital CommunicationsCorporation, permit many communications to be transmitted over the samebandwidth, thereby greatly increasing the capacity of the RF spectrum.In B-CDMA™ brand communication systems, an information signal at thetransmitter is mixed with a pseudo random “spreading code” which spreadsthe information signal across the entire bandwidth which is employed bythe communication system. The spread signal is upconverted to an RFsignal for transmission. A receiver, identified by the pseudo randomspreading code, receives the transmitted RF signal and mixes thereceived signal with an RF sinusoidal signal generated at the receiverby a first-stage local oscillator to downconvert the spread spectrumsignal. The spread information signal is subsequently mixed with thepseudo random spreading code, which has also been locally generated, toobtain the original information signal.

[0005] In order to detect the information embedded in a received signal,a receiver must use the same pseudo random spreading code that was usedto spread the signal. All signals which are not encoded with the pseudorandom code of the receiver appear as background noise to the receiver.Accordingly, as the number of users that are communicating within theoperating range of a particular communication station increases, theamount of background noise also increases, making it difficult forreceivers to properly detect and receive signals. The transmitter mayincrease the power of the transmitted signal, but this will increase thenoise (interference) as seen by other receivers.

[0006] Applicants have recognized the need to decrease the amount ofinterference in order to increase the capacity (number of users) of theCDMA system.

SUMMARY

[0007] A communication station for use in a CDMA communication system isprovided with an antenna system which includes a plurality of antennasfor receiving CDMA communication signals. The antennas are coupled to asummer, which outputs a summed signal from the antenna system. One ofthe antennas is directly coupled to the summer. Each of the otherantennas is coupled to a respective delay unit which imparts apredetermined fixed delay to the signals received by the respectiveantennas. Each delay unit is in turn coupled to the summer. The antennasystem, accordingly, outputs a summed signal which has a known phasedistortion corresponding to the fixed delays imparted by the delayunits.

[0008] A receiver is coupled to the antenna system summer output, stripsthe carrier frequency, and passes the resultant summed baseband signalto one or more modems. Where the communication station is designed toreceive communications associated with a single dedicated CDMA code,such as a subscriber station, a single modem is preferred. Wheremultiple communications are to be simultaneously processed, such as in abase station or a subscriber unit which serves multiple users or as anemulated base station, multiple modems are provided.

[0009] Each modem is configured to receive an individual communicationsignal contained within the baseband signal associated with unique CDMAcodes. The modems include circuitry for compensating for at least theknown signal phase distortion imparted by the delay units. Preferably,each modem includes a vector correlator (also known as a rake receiver)for determining filter coefficients which are passed to an adaptivematched filter (AMF). The AMF is a transversal filter which uses thecoefficients to overlay delayed replicas of the signal onto each otherto provide a filtered signal having increased signal-to-noise ration(SNR).

[0010] The vector correlator/rake receiver has a sufficient capacity todetermine filter coefficients over a window of time which is at least aswide as the known delays created by the antenna system. Preferably,three antennas are used, first, second and third. The second antenna'ssignal is delayed to provide a signal replica with a three-chip delayrelative to the signal replica provided by the first antenna. The thirdantenna's signal is delayed to provide a signal replica having aseven-chip delay relative to the signal replica provided by the first.In order to process the delayed replicas of the signal which originatedwith the second and third antennas, the vector correlator/rake receiverprocesses information in at least an eleven chip window. The processingof the fourth and eighth chips within the window, accordingly, providescoefficients to compensate for the distortion imparted by the threeandseven-chip delays of the second and third antenna signals.

[0011] The use of rake receivers to compensate for multipath distortionof a CDMA signal is disclosed in U.S. patent application Ser. Nos.08/266,769 and 08/871,109 which are incorporated herein as if fully setforth. It will be recognized to those who are of skill in the art thatthe utilization of a rake receiver or a vector correlator will providecompensation for not only multipath distortion, but also for the knowndistortion imparted by the multi-antenna system disclosed herein.

[0012] The gain of the signal output by the AMF is monitored by anautomatic power control (APC) which relays messages to the transmittingstation to control the power of the transmitted signal. Since the vectorcorrelator or rake receiver compensates for both multipath phasedistortion as well as the known distortion imparted by the antennasystem, an enhanced gain is realized in comparison to a single antennasystem where only multipath phase distortion is compensated for.Accordingly, the relatively higher gain which is received enables theAPC to direct the transmitting station to lower its power thusincreasing the capacity of the overall CDMA system.

[0013] Where the physical site of the communication station requires ormakes the location of the antenna system desirable at a locationrelatively distant to the processing components, applicants' haverecognized that significant loss in signal strength can occur. Toaddress this problem the receiver/transmitter (RxTx) may be physicallyseparated from the other processing compartments. The RxTx may then belocated in relative proximity to the remotely located antennas andrelatively distant to the processing modems. A significant improvementin signal strength is seen by the elimination of twenty feet or more ofconnecting cable between the antenna system and the RxTx. Accordingly,where remote location of the antenna or antenna system is necessary, atleast twenty feet of cable is provided to couple the RxTx to the othersignal processing equipment permitting the RxTx to be mounted in closerproximity and coupled to the antenna system with a relatively shortcable. Preferably, the signal coupling cable which connects the RxTx tothe other signal processing equipment includes DC power to provide powerto the RxTx.

[0014] Other aspects and advantages will become apparent to thoseskilled in the art after reading the detailed description of thepreferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a schematic illustration of a communication networkembodiment of the present invention.

[0016]FIG. 2 is a schematic illustration of the propagation of signalsbetween a base station and a plurality of subscriber units.

[0017]FIG. 3 is a block diagram of a first embodiment of a communicationstation made in accordance with the teachings of the present invention.

[0018]FIG. 4 is a more detailed block diagram of a first embodiment of acommunication station made in accordance with the teachings of thepresent invention.

[0019]FIG. 5 is a schematic illustration of the vector correlator of thecommunication station shown in FIG. 4.

[0020]FIG. 6 is a schematic illustration of the phase locked loop of thecommunication station shown in FIG. 4.

[0021]FIG. 7 is a block diagram of a second embodiment of acommunication station made in accordance with the teachings of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Presently preferred embodiments are described below withreference to the drawing figures wherein like numerals represent likeelements throughout.

[0023] A communication network 2 embodying the present invention isshown in FIG. 1. The communication network 2 generally comprises one ormore base stations 4, each of which is in wireless communication with aplurality of subscriber units 6, which may be fixed or mobile. Eachsubscriber unit 6 communicates with either the closest base station 4 orthe base station 4 which provides the strongest communication signal.The base stations 4 also communicates with a base station controller 8,which coordinates communications among base stations 4. Thecommunication network 2 may also be connected to a public switchedtelephone network (PSTN) 9, wherein the base station controller 8 alsocoordinates communications between the base stations 4 and the PSTN 9.Preferably, each base station 4 communicates with the base stationcontroller 10 over a wireless link, although a land line may also beprovided. A land line is particularly applicable when a base station 4is in close proximity to the base station controller 8.

[0024] The base station controller 8 performs several functions.Primarily, the base station controller 8 provides all of the operations,administrative and maintenance (OA&M) signaling associated withestablishing and maintaining all of the wireless communications betweenthe subscriber units 6, the base stations 4, and the base stationcontroller 8. The base station controller 8 also provides an interfacebetween the wireless communication system 2 and the PSTN 9. Thisinterface includes multiplexing and demultiplexing of the communicationsignals that enter and leave the system 2 via the base stationcontroller 8. Although the wireless communication system 2 is shownemploying antennas to transmit RF signals, one skilled in the art willrecognize that communications may also be accomplished via microwave orsatellite uplinks.

[0025] Referring to FIG. 2, the propagation of signals between abasestation 4 and a plurality of subscriber units 6 is shown. A two-waycommunication channel 11 comprises a signal transmitted 13 (TX) from thebase station 4 to subscriber station 6 and a signal received 15 (RX) bythe base station 4 from the subscriber unit 6. The signal between thebase station 4 and the subscriber unit 6 include the transmission of apilot signal. The pilot signal is a spreading code which carries no databits. The pilot signal is used for synchronizing the transmissionbetween the base station 4 and subscriber unit 6. Transmission andreception of data begins after synchronization of the subscriber unit 6and the base station 4.

[0026] Referring to FIG. 3, a communication station 100, which may beeither a base station 4 or a subscriber unit 6, includes an antennasystem 110 having a plurality of antennas 120, delay units 130 and asummer 135. The summer 135 is coupled to an RF receiver of areceiver/transmitter (RxTx) unit 140 via a cable 142. An RF transmitoutput of the RxTx 140 is coupled to one of the antennas 120, preferablythe first antenna, by a direction coupler 144 and connecting cable 146.The RxTx 140 is connected to signal processing equipment 148 whichincludes one or more of modems 150 via a cable 152. Preferably, theantenna system 110, RxTx 140 and the other signal processing equipment148 are in close proximity to each other to inhibit loss of signalstrength. However, if it is necessary to place the antenna system 110 ina location remote from the signal processing equipment, for example morethan 20 feet away, significant loss in signal level can result duringtransmission and reception. Applicants have recognized that thesusceptibility to loss in signal strength can be significantly reducedby physically separating the RxTx 140 from the other signalingprocessing components 148 including the modems 150 to permit arelatively short cables 142, 146 to couple the RxTx and the antennasystem 110 and a relatively long cable 152 to couple the RF receiver 140to the other processing equipment 148. Where separation of the units140, 148 is desirable, preferably, the coupling cable 152 is at leasttwenty feet long to permit a reduction in the length of cables 142, 146required to couple the RxTx 140 to the antenna system 110. To facilitatethe location of the RxTx 140 in proximity with the antenna system 110,it is preferred that connecting cable 152 provide the DC power to theRxTx 140 from the other processing equipment 148 which includes modems150. This may be accomplished by overlaying the DC power on the signalsto be transmitted.

[0027] Separate delay units 130 shift the time-of-arrival of the signalreplicas to the receiver. The resulting combined signal will have Ncopies of the received signal with different time delays wherein N is aninteger. Preferably, each delay unit 130 results in a delay of at leasttwo chips which enables further processing to achieve a net increase insignal strength.

[0028] The resulting combined signal is output by the summer 135 to theRF receiver of the RxTx 140. The RF receiver of the RxTx 140 strips thecarrier frequency and passes a resulting baseband signal to the modems150. The signal received by each modem 150 has a distortioncorresponding to the delays imparted by the delay units 130. The signalsmay also have distortion attributable to multipath occurring naturallyin the channel 120.

[0029] As is known in the art, each CDMA communication is associatedwith a unique code. Multiple modems 150 enable simultaneous processingof multiple CDMA communications, each processing a communicationassociated with a different CDMA code. For subscriber units a singlemodem 150 may be used if only a single communication is to be supportedat any given time. However, subscriber units may have several modems tosupport multiple communications or to serve as an emulated base station.As explained below, combining N signals with a known distortion enablesthe lowering of the transmit power required by the receiving units. As aresult, this increases the number of subscribers 6 or the number ofsimultaneous communications with a base station 4 within the system.

[0030] Referring to FIG. 4, a communication station 200 is illustratedhaving an antenna system 205 containing three antennas 120, 120 a, 120b, two delay units 130 a, 130 b and one summer 135. This particularconfiguration permits an increase in up to 4.77 dB of gain in a receivedsignal as compared with a single antenna unit which receives a signaltransmitted at the same power. This gain translates into increasedcapacity (increased subscribers or increased number of simultaneouscommunications), which can be handled by communication station 200,since the transmit power can be reduced.

[0031] The three antennas 120, 120 a, 120 b are preferably spaced atleast six wavelengths apart, or equivalently, a few inches to a fewyards from each other so that the antenna diversity gain is avoided bythe arrangement. The antennas 120, 120 a, 120 b are preferably locatedso as to receive the CDMA communication signals from independentpropagation paths.

[0032] The summation unit 135 receives a signal from the first antenna120 with no delay. The summation unit 135 receives a signal from thesecond antenna 120 a via delay unit 130 a which imparts a delay of threechips relative to the first antenna's signal. The summation unit 135also receives a signal from the third antenna 120 b via delay unit 130 bwhich imparts a delay of seven chips relative to the first antenna'ssignal. The signal delay provided is typical, but can be changed by onehaving ordinary skill in the art, and is influenced by the temporalwidth of the vector correlator/rake receiver.

[0033] The delay units may comprise electronic circuitry, for example astanding acoustic wave (SAW) device, or simply be a selectively extendedpiece of cable coupling the antennas to the mixer 135, which isselectively extended to provide for desired delay. As explained below,benefits in increased gain are realized as long as the delays impartedare at least two chips and the vector correlator and/or rake receiverwhich analyzes the distortion has sufficient capacity to analyze the netdelays imparted by all of the delay units.

[0034] The signal from all three antennas 120, 120 a, 120 b are added bythe summer 135 then passed to an RF receiver 207 to strip the carrierfrequency. The resulting baseband signal has three copies of thereceived communication signal, each copy having a different delay.

[0035] The baseband signal output by the receiver 207 is processed bythe modems 150. Delayed replicas of the communication signal areessentially combined by overlaying them with the correct phase andamplitude which results in increased gain. This function is performed byan adaptive matched filter (AMF) 250 which operates in accordance withfilter coefficients determined by a vector correlator 230 in conjunctionwith a carrier recovery phase lock loop 240. The three antenna system110 generally provides a gain of 3 to 4 dB and ideally 4.77 dB ascompared to a similar receiving station employing a single antenna.Therefore, there is generally a reduction of 3 to 4 dB in transmit powerrequired to process communication.

[0036] The modem 150 includes an analog to digital converter 210 whichconverts the baseband signal into a digital signal with the assistanceof a tracker 220. The tracker 220 directs the digital converter 210 tosample the strongest analog representation of the data being transmittedto the communication station 200 to provide an accurate digital signal.The digital signal includes both a digital data signal and a digitalpilot signal.

[0037] As is well known in the art, CDMA communication stations receivea pilot signal to provide synchronization of a locally generated pseudorandom code with the pseudo random code transmitted by the transmittingstation, and to provide a transmission power reference during initialpower ramp-up. Typically, a base station transmits the pilot signal toprovide synchronization of a locally generated pseudo random code withthe transmitted pseudo random code. The pilot signal is a sequence ofpseudo random complex numbers which are modulated in this system byconstant complex pilot value having a magnitude of one and phase ofzero.

[0038] The digital pilot signal will have the same phase distortion asthe digital data signal, since they are both contained within thebaseband signal. Accordingly, the vector correlator 230 receives thepilot signal and determines in conjunction with a phase lock loop 240,filter coefficients based on the distortion of the pilot signal. Hence,the determined coefficients also represent the distortion of the datasignal. The data signal/CDMA communication signal, which is directed tothe adaptive match filter (AMF) 250, is processed by the AMF inaccordance with the filter coefficients generated by the vectorcorrelator in combination with the phase lock loop.

[0039] As disclosed in U.S. patent application Ser. Nos. 08/266,769 and08/871,109, vector correlators/rake receivers in conjunction with phaselock loop circuitry have been utilized to produce filter coefficients tocorrect for multi-path distortion. As used in the present invention, thevector correlator and phase lock loop generate filter coefficientsassociated with both natural multipath distortion and the artificiallyintroduced distortions imparted by the antenna system 130 a, 130 b, solong as the delays of the antenna system are within the correctionwindow used by the vector correlator 230.

[0040] Referring to FIG. 5, the vector correlator 230 provides anestimate of the complex impulse response, having real and imaginarycomponents, of the channel over which the communication signal istransmitted including the antenna array in the present invention. Thevector correlator 230 has a plurality of independent elements231.1,231.2, 231 i, preferably eleven, wherein the pilot pseudo randomcode input to each element is delayed by one chip to define a processingwindow of eleven chips.

[0041] Each element 231 performs an open loop estimation of the sampledimpulse response of the RF channel. Thus, the vector correlator 230produces noisy estimates of the sampled impulse response at evenlyspaced intervals. The signal analysis performed by the vector correlator230 accordingly determines phase and amplitude distortions occurring atdifferentpoints within the processing window. Since known delays ofthreechips and seven chips have been imparted by delay units of 130 a, 130 b,the vector correlator will determine the existence of copies of thesignal at chip zero, chip three and chip seven. Where the receivedsignal also includes a five chip, for example, delayed replicaattributable to natural multipath, the vector correlator will determinesignal copies at zero, three, five, seven and eight chips. As will berecognized by those of ordinary skill in the art, providing the vectorcorrelator with a wider window, for example, twenty-one chips, wouldresult in the above example determining copies of the signal at zero,three, five, seven, eight and twelve. Preferably the vector correlatorhas a wide enough window to accommodate all of the delays imparted bythe antennas within the antenna system 205. In the above example, if thevector correlator processing window is less than eleven, the signalreceived by antenna 120 b will not be fully compensated for.

[0042] In operation, each element of the vector correlator 230 receivesa locally generated pseudo random pilot code. The signal supplied to thevector correlator 230 from the analog digital converter 210 is input toeach element. Mixers 232 mix the locally generated pseudo random codewith the pilot to despread the pilot signal. Delay units 233 impart aone chip delay on the pilot code in all but one element 231. Eachelement 231 receives a carrier- offset-phase-correcting signal fromphased lock loop 240, which is mixed with the despread pilot signal ineach element 231 by mixers 233 to provide sample impulse responseestimates. The vector correlator 230 further includes a plurality of lowpass filters 234 which are connected to each mixer 233 and which smootheach corresponding sample impulse response estimate. The complexconjugates of each smoothed sampled impulse response estimate are usedas the filter coefficients or weights for the adaptive match filter 250.In addition, the complex conjugate of each smoothed sampled response ismixed with the despread pilot signal by mixers 235. The summation unit236 receives the outputs of mixers 235 and outputs the combined despreadpilot signal which is now corrected for multipath distortion.

[0043] The carrier recovery phase lock loop 240 acts upon the despreadpilot signal to estimate and correct the phase error due to RF carriersignal offset. The offset may be due to internal componentmismatchesorto channel distortion. Component mismatches between the subscriberoscillator and the receiver oscillator may cause slightly differentoscillator outputs. These component mismatches can be furtherexacerbated by local and environmental conditions, such as the heatingand cooling of electronic components, which may cause performancechanges in the components. With respect to channel distortion, dopplereffects caused by the motion of the receiving stations relative to thetransmitter station or a multipath reflector may cause the RF carrier tobecome distorted during transmission. This may also result in a RFcarrier offset.

[0044] The phase lock loop 240 is preferably implemented in aprogrammable digital signal processor. The phase lock loop 240 monitorsthe output of vector correlator 230 to estimate and correct for a phaseerror due to RF offset, thereby providing acceptable quality.

[0045] Referring to FIG. 6, the continuously adjusted-bandwidth PLLcomprises a mixer 241, a normalizing unit 242, and arctangent analyzer243, a phased lock loop filter 244, a voltage controlled oscillator 245and a bandwidth control section 246. The mixer 241 receives its inputfrom the vector correlator 230 which is the despread pilot signalprocessed to correct for channel distortion due to multipath effects.The despread pilot signal is mixed with a correction signal from voltagecontrolled oscillator 245 to produce a complex error signal, which istransmitted to normalizing unit 242. The normalized signal is then inputinto arctangent analyzer 243. The output of the arctangent analyzer 243is a quantized phase angle of the complex error signal. The bandwidthcontrol section 246 continuously monitors the quantized phase errorsignal and generates a control signal to control the bandwidth of aphased lock loop filter 244. The signal output for the phased lock loopfilter is transmitted to the voltage controlled oscillator 245. Thevoltage controlled oscillator 245 outputs a signal to mixer 241 andvector correlator 230, which is indicative of a carrier-offsetphase-error. This entire process is repeated until a complex errorsignal output from the mixer 241 is at a minimum. Optimum performance ofthe modem 150 will not occur until the vector correlator 230 and phaselock loop 240 have reached a mutually satisfactory equilibrium point.

[0046] The vector correlator 230 outputs in conjunction with the carrierrecovery phase lock loop 240 filter coefficients to the adaptive matchedfilter 250. The adaptive matched filter 250 is then able to process thecommunication signal to compensate for channel distortion due to bothmultipath effects and the antenna system. This compensation increasesthe gain of the signal by, in effect, overlaying delayed replicas of thesignal. The adaptive matched filter 250 transmits the filtered resultingsignal to the traffic despreaders 260 and auxiliary despreader 270. TheAPC 290 determines whether the signal strength of the transmitted signalshould be increased or decreased to maintain an appropriate bit errorrate based upon the estimate of the signal strength resulting from thetraffic despreader 270. This information is transmitted from thecommunication station 200 to the station which transmitted the signal.

[0047] The traffic despreaders 260 transmit the despread filteredresultant signal to the Viterbi decoder 280 which function as describedin copending application Ser. No. 08/871,008 which is incorporated byreference as if fully set forth of the convolutional encoder (not shown)of a subscriber unit 6. The Viterbi decoder 280 passes the resultingsignal to a digital to analog converter 300 which provides for an outputto the user. For data communications, a digital output may be provided.

[0048] An alternative embodiment of the antenna system present inventionis shown in FIG. 7. The antenna system 400 shown in FIG. 7 may besubstituted for the antenna system 205 shown in FIG. 4. The antennasystem 400 includes three antennas 410 a, 410 b, 410 c. The firstantenna 410 a is coupled to a first summer 450 by way of a firstbandpass filter 420 a, a first low noise amplifier 430 a and a firstdelay unit 440. A second antenna 410 b is coupled to the first summer450 by way of a second bandpass filter 420 b, a second low noiseamplifier 430 b and a first attenuator 460 b. The CDMA signals receivedby way of the first and second antennas 410 a, 410 b are summed bysummer 450 are then passed to a second summer 480 by way of a delay unit470. The third antenna 410 c is coupled to the second summer 480 by wayof a third bandpass filter 420 c, a third low noise amplifier 430 c anda second attenuator 460 c. A CDMA signal received by the third antenna410 c is summed with the output of the delay unit 470. Accordingly, theantenna system 400 outputs a signal including a known distortioncorresponding to the fixed delays imparted by the delay units 440 and470. It should be recognized by those of skill in the art that thisantenna system 400 achieves the same result as the antenna system 205shown in FIG. 4.

[0049] Although the invention has been described in part by makingdetailed reference to certain specific embodiments, such detail isintended to be instructive rather than restrictive. It will beappreciated by those skilled in the art that many variations may be madein the structure and mode of operation without departing from the spiritand scope of the invention as disclosed in the teachings herein.

What is claimed is:
 1. A CDMA subscriber unit comprising: a plurality ofselectively spaced omnidirectional antennas, each for receiving CDMAcommunication signals within the operating range of the subscriber unit;a summer associated with said antennas and having an output foroutputting a combined signal; a first of said antennas directly coupledto said summer; each subsequent antenna of said plurality of antennasassociated with a respective delay unit, each respective delay unitbeing coupled to said summer and each respective delay unit imparting adifferent fixed delay to the signal received by the respective antenna,each fixed delay resulting in a delay of at least two chips relative toeach other delay; the delayed signals being combined with the signal ofsaid first antenna by said summer, said combined output signal having aknown phase distortion corresponding to the fixed delays; a receivercoupled to the output of said summer; and a modem for receiving anindividual communication signal associated with a unique CDMA code, saidmodem including distortion-compensating means for compensating for atleast said known phase distortion.
 2. The subscriber unit of claim 1wherein said antenna system includes three antennas, a second of saidantennas being associated with a first delay unit which imparts a firstdelay to the signal received by said second antenna, a third of saidantennas being associated with a second delay unit which imparts asecond delay to the signal received by said third antenna whereby saidknown phase distortion of said summer output corresponds to thepredetermined delays imparted by said first and second delay units. 3.The subscriber unit of claim 2 wherein the delay imparted by said firstdelay unit results in a three chip delay and the delay imparted by saidsecond delay unit results in a seven chip delay.
 4. The subscriber unitof claim 3, wherein said modem includes a vector correlator forgenerating filter coefficients for an adaptive matched filter based onsignal distortion determined by said vector correlator; said vectorcorrelator having a processing capacity of at least eleven chips wherebysaid vector correlator compensates for said known distortion and formultipath distortion ascertainable within its processing capacity; andsaid adaptive matched filter processing communication signals with saidunique CDMA code using coefficients generated by said vector correlator.5. The subscriber unit of claim 4 wherein said modem further comprisesan automatic power control unit associated with said adaptive matchfilter for generating a return power control signals for transmission.6. The subscriber unit of claim 2 wherein said antennas are spaced atleast six wavelengths apart from each other.
 7. The subscriber unit ofclaim 2 wherein said antennas are spaced no more than three yards apartfrom each other.
 8. The subscriber unit of claim 2 wherein said receiverand said modem are located in physically separate units and furthercomprising a cable for coupling said modem to said receiver, said cableproviding power to said receiver.
 9. The subscriber unit of claim 8wherein said cable is at least 20 feet long.
 10. A subscriber unithaving an antenna system comprising: a plurality of single beam,omnidirectional antennas, each for receiving CDMA communication signalswithin the operating range of the subscriber unit; a summer associatedwith said antennas and having an output for outputting a combinedsignal; a first antenna of said plurality of antennas coupled to saidsummer; a first delay unit coupled to said summer and a second antennaof said plurality of antennas for delaying and outputting said CDMAcommunication signals from said second antenna; said summer combiningsaid output from said first delay unit and said signals received by saidfirst antenna, said combined signal comprising at least two copies ofthe received signal by said plurality of antennas; and a modem forreceiving an individual communication signal associated with a uniqueCDMA code within said combined signal.
 11. The subscriber unit of claim10 further comprising a receiver coupled to said antenna system and saidmodem.
 12. The subscriber unit of claim 11 wherein said combined signalfurther comprises a known distortion corresponding to at least saidfirst fixed delay.
 13. The subscriber unit of claim 12 wherein each ofsaid plurality of antennas, except said first antenna, is associatedwith a respective delay unit which is coupled to said summer.
 14. Thesubscriber unit of claim 13 wherein said known distortion of saidcombined signal corresponds to all of said delay units.
 15. Thesubscriber unit of claim 14 wherein said receiver is a physicallyseparate unit from said modem, and said subscriber unit furthercomprises a cable for coupling said modem to said receiver includingpower conductors for supplying power from said modem unit to saidreceiver unit.
 16. The subscriber unit of claim 15 wherein said cable isat least 20 feet long.
 17. The subscriber unit of claim 10 wherein saidmodem includes a vector correlator for generating filter coefficientsfor an adaptive matched filter based on signal distortion determined bysaid vector correlator; said vector correlator having a processingcapacity at least equal to a predetermined chip delay corresponding tosaid known distortion whereby said vector correlator compensates forsaid known distortion and for multipath distortion ascertainable withinits processing capacity; and said adaptive match filter processingindividual communication signals associated with said unique CDMA codeusing coefficients generated by said vector correlator whereby increasedsignal gain is realized which is attributable in part to thecompensation for said known distortion.
 18. The subscriber unit of claim17 wherein said modem further comprises an automatic power control unitassociated with said adaptive match filter for generating power controlsignal for transmission.
 19. The subscriber unit of claim 10 furthercomprising: a plurality of modems coupled to said receiver, each modemfor receiving an individual communication signal associated with aunique CDMA code, such that multiple communications received via saidreceiver can be simultaneously processed, each said modem includingdistortion compensating means for compensating for at least said knownsignal distortion.
 20. An antenna system for use in a CDMA subscriberunit comprising: first, second and third single beam, omnidirectionalantennas; each for receiving CDMA communication signals within theoperating range of the subscriber unit; a first summer coupled to saidfirst and second antennas, for combining said signals received by saidfirst and second antennas, whereby said combined signal comprises twocopies of the received signal; said first antenna coupled to said summerby way of a first delay unit; a second summer coupled to said firstsummer by way of a second delay unit, and coupled to said third antenna,for combining signals received by said third antenna with said combinedsignal output by said first summer and outputting a second combinedsignal; and a modem for detecting an individual communication signalassociated with a unique CDMA code within said second combined signal.21. An antenna system for use in a subscriber unit comprising: aplurality of selectively spaced omnidirectional antennas, each forreceiving CDMA communication signals within the range of the subscriberunit; a summer associated with said antennas and having an output foroutputting a combined signal; a first of said antennas directly coupledto said summer; each subsequent antenna of said plurality of antennasassociated with a respective delay unit, each respective delay unitbeing coupled to said summer and each respective delay unit imparting adifferent fixed delay to the signal received by the respective antenna,each fixed delay resulting in a delay of at least two chips relative toeach other delay; the delayed signals being combined with the signal ofsaid first antenna by said summer, said combined output signal having aknown phase distortion corresponding to the fixed delays; and a modemfor receiving an individual communication signal associated with aunique CDMA code, said modem including distortion-compensating means forcompensating for at least said known phase distortion.
 22. The antennasystem of claim 21 further including three antennas, a second of saidantennas being associated with a first delay unit which imparts a firstdelay to the signal received by said second antenna, a third of saidantennas being associated with a second delay unit which imparts asecond delay to the signal received by said third antenna, whereby saidknown phase distortion of said summer output corresponds to the delaysimparted by said first and second delay units.
 23. The antenna system ofclaim 22 wherein the delay imparted by said first delay unit results ina three chip delay and the delay imparted by said second delay unitresults in a seven chip delay.
 24. The antenna system of claim 23wherein: said modem includes a vector correlator for generating filtercoefficients for an adaptive matched filter based on signal distortiondetermined by said vector correlator; said vector correlator having aprocessing capacity of at least eleven chips whereby said vectorcorrelator compensates for said known distortion and for multipathdistortion ascertainable within its processing capacity; and saidadaptive match filter processing communication signals with said uniqueCDMA code using coefficients generated by said vector correlator.